The present invention relates to an airbag apparatus for a vehicle for protecting an occupant of the vehicle in the case of a collision.
Typical airbag apparatuses have a retainer to which an airbag is connected, an inflator for generating gas for inflating the airbag, and a cover for covering the airbag. The inflator generates gas to inflate the airbag in a car crash. The airbag opens the cover to inflate into the interior of a vehicle.
Certain airbag apparatuses include a vent hole. When an occupant hits against an inflated airbag, gas in the airbag flows out through the vent hole to absorb impact applied to the occupant.
In general, the vent hole is kept closed until the inner pressure of the airbag increases to a predetermined level in order to prevent the gas from flowing out early through the vent hole. U.S. Pat. Nos. 6,158,770 and 5,743,558 (both incorporated by reference herein) disclose a vent hole having a valve for closing the vent hole. The valve is opened by a drive unit. The drive unit, however, increases the weight of an airbag apparatus and also increases the cost.